The invention relates to the field of optical components. More specifically, the invention relates to maintaining alignment of a laser diode with an optical fiber.
An important aspect of optical components, such as optical components used in telecommunications and data communications technology (i.e., lightwave communications), is the alignment of a light source with a light transmission medium. For example, a semiconductor laser aligned with an optical fiber. Because the light emitted from the semiconductor laser is transmitted via the optical fiber, the alignment between the semiconductor laser and the optical fiber is an important aspect of the optical components.
The alignment of the semiconductor laser with the optical fiber is commonly referred to as coupling. The efficiency of the transmission of power from one medium to another (i.e., semiconductor laser to optical fiber) is commonly referred to as coupling efficiency.
Prior to operation, aligning a semiconductor laser with an optical fiber may have low coupling efficiencies, approximately 10% corresponding to a loss in power of approximately 10 decibels. The low coupling efficiencies may be attributable to factors such as size and shape differences in spot sizes between the semiconductor laser and the optical fiber, absorption, reflectance, scattering, tolerances of the components and alignment methods involved, and so forth. With so many factors contributing to low coupling efficiencies, a great deal of effort is expended to increase the coupling efficiencies and reduce the loss in power.
Efforts to increase the coupling efficiencies may involve focusing the light from the semiconductor laser to the optical fiber, modifying the optical fiber end, through which the optical fiber receives the light, reducing the tolerances, and so forth. Additionally, certain thermal methods of attaching the optical fiber on an optical fiber mounting block may affect the alignment. The efforts involved in increasing the coupling efficiencies and reducing the power loss often correspond to increases in costs, complexity, and size. As a result, once a desired coupling efficiency is achieved, maintaining the desired coupling efficiency is important. However, maintaining the desired coupling efficiency during operation is difficult.
During operation, maintaining the desired coupling efficiency can be difficult due to many factors. One factor, in particular, is the thermal characteristics of materials involved in the optical components.
For example, the semiconductor laser may have a temperature characteristic, whereby, during operation, as the temperature of the semiconductor laser increases, the required operating current of the semiconductor laser also increases. In order to control the temperature of the semiconductor laser, the semiconductor laser may be mounted on a heatsink, where the heatsink conducts heat away from the semiconductor laser at a rate corresponding to the thermal conductivity of the material of the heatsink. Because the heatsink absorbs the heat from the semiconductor laser, the heatsink increases in temperature, as well. Subsequently, the heat in the heatsink, itself, must be removed or the rate at which the heat is transferred from the semiconductor laser to the heatsink will decrease, and ultimately stop.
Additionally, the alignment between the semiconductor laser and the optical fiber may change due to thermal properties of the heatsink, such as the coefficient of thermal expansion (CTE). The CTE is a thermal property of a material describing dimensional changes corresponding to temperature changes in the material.
One method for removing the heat from the semiconductor laser may involve an active heat removal device, such as, a Peltier effect device. Due to size constraints of optical components, active heat removal methods result in increased complexity and cost.
As described above, due to the many factors affecting coupling efficiencies, changes in alignment, due to thermal properties of the optical components, may result in power loss between the semiconductor laser and the optical fiber.